*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
    --bg:#0B1020;--bg-card:#151C33;--bg-card-hover:#1a2340;
    --primary:#4F8CFF;--accent:#6CF6FF;--secondary:#8B5CFF;
    --success:#42D392;--warning:#FFB84D;--danger:#FF5E7A;
    --text:#E2E8F0;--text-muted:#8892A8;--text-heading:#FFF;
    --border:rgba(79,140,255,.12);--glow:rgba(79,140,255,.15);
    --radius:12px;--radius-lg:16px;--tr:200ms ease;
}
html{font-size:16px}
body{font-family:'Inter',system-ui,sans-serif;background:var(--bg);color:var(--text);min-height:100vh;-webkit-font-smoothing:antialiased}
a{color:var(--primary);text-decoration:none}

/* Layout */
.lesson-shell{max-width:640px;margin:0 auto;min-height:100vh;display:flex;flex-direction:column}
.top-bar{display:flex;align-items:center;gap:10px;padding:12px 16px;position:sticky;top:0;background:rgba(11,16,32,.92);backdrop-filter:blur(12px);z-index:10;border-bottom:1px solid var(--border)}
.exit-btn,.back-btn{width:32px;height:32px;min-width:32px;border-radius:8px;border:1px solid var(--border);background:none;color:var(--text-muted);cursor:pointer;display:flex;align-items:center;justify-content:center;transition:all var(--tr);flex-shrink:0}
.exit-btn:hover{border-color:var(--danger);color:var(--danger)}
.back-btn:hover{border-color:var(--primary);color:var(--primary)}
.back-btn{display:none}
.progress-track{flex:1;height:6px;background:rgba(255,255,255,.06);border-radius:3px;overflow:hidden;min-width:0}
.progress-fill{height:100%;background:var(--primary);border-radius:3px;transition:width .4s ease}
.xp-badge{font-size:.75rem;font-weight:700;color:var(--accent);white-space:nowrap;display:flex;align-items:center;gap:4px;flex-shrink:0}
.xp-icon{height:2.4em;vertical-align:middle;display:inline-block}

/* Card */
.card-area{flex:1;display:flex;align-items:center;justify-content:center;padding:24px 20px}
.card{width:100%;background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius-lg);padding:40px 32px;opacity:0;transform:translateY(16px);transition:opacity .35s ease,transform .35s ease}
.card.visible{opacity:1;transform:translateY(0)}
.card.exit{opacity:0;transform:translateY(-16px)}
.card-label{font-size:.6875rem;font-weight:600;text-transform:uppercase;letter-spacing:.1em;color:var(--primary);margin-bottom:12px;padding-right:52px}
.card h2{font-size:1.375rem;font-weight:700;color:var(--text-heading);line-height:1.3;margin-bottom:16px}
.card p{font-size:.9375rem;color:var(--text);line-height:1.7;margin-bottom:16px}
.card p:last-child{margin-bottom:0}
.highlight{color:var(--accent);font-weight:600}
.card .fact{background:rgba(108,246,255,.06);border:1px solid rgba(108,246,255,.15);border-radius:10px;padding:16px;margin:16px 0;font-size:.875rem;color:var(--accent);line-height:1.6}

/* Buttons */
.btn{display:inline-flex;align-items:center;justify-content:center;padding:12px 28px;border-radius:10px;font-size:.9375rem;font-weight:600;border:none;cursor:pointer;font-family:inherit;transition:all var(--tr)}
.btn-primary{background:var(--primary);color:#fff}
.btn-primary:hover:not(:disabled){background:#6BA0FF;box-shadow:0 0 20px var(--glow)}
.btn-primary:disabled{opacity:.5;cursor:default}
.btn-reading{background:rgba(79,140,255,.3) !important;font-variant-numeric:tabular-nums}
.btn-ghost{background:transparent;color:var(--text-muted);border:1px solid var(--border)}
.btn-ghost:hover{color:var(--text);border-color:rgba(255,255,255,.2)}
.card-actions{display:flex;gap:12px;justify-content:center;margin-top:24px}

/* Quiz options */
.options{display:flex;flex-direction:column;gap:10px;margin-top:20px}
.option{padding:14px 18px;background:rgba(255,255,255,.03);border:2px solid var(--border);border-radius:10px;cursor:pointer;transition:all var(--tr);font-size:.9375rem;color:var(--text);text-align:left}
.option:hover{border-color:rgba(79,140,255,.4);background:rgba(79,140,255,.05)}
.option:focus-visible,.match-item:focus-visible{outline:3px solid var(--accent);outline-offset:3px}
.option.correct{border-color:var(--success);background:rgba(66,211,146,.1);color:var(--success)}
.option.wrong{border-color:var(--danger);background:rgba(255,94,122,.08);color:var(--danger)}
.option.disabled{pointer-events:none;opacity:.5}

/* Match game */
.match-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:20px}
.match-item{padding:12px;background:rgba(255,255,255,.03);border:2px solid var(--border);border-radius:10px;text-align:center;font-size:.875rem;font-weight:600;cursor:pointer;transition:all var(--tr);color:var(--text);user-select:none;position:relative}
.match-item[data-side="q"]{border-left:3px solid var(--danger);background:rgba(255,94,122,.04)}
.match-item[data-side="a"]{border-left:3px solid var(--success);background:rgba(66,211,146,.04)}
.match-item.active{border-color:var(--primary);background:rgba(79,140,255,.1);color:var(--primary)}
.match-item.matched{pointer-events:none}
.match-myths .match-item.matched[data-side="q"]{text-decoration:line-through;text-decoration-color:var(--danger);text-decoration-thickness:2px}

/* Feedback */
.feedback{margin-top:16px;padding:14px 18px;border-radius:10px;font-size:.875rem;line-height:1.5;display:none}
.feedback.show{display:block}
.feedback.success{background:rgba(66,211,146,.1);border:1px solid rgba(66,211,146,.3);color:var(--success)}
.feedback.error{background:rgba(255,94,122,.08);border:1px solid rgba(255,94,122,.25);color:var(--danger)}
.feedback .hint{color:var(--warning);margin-top:8px;font-style:italic}

/* Bonus sections */
.bonus-trigger{display:flex;align-items:center;gap:8px;padding:12px 16px;background:rgba(139,92,255,.08);border:1px solid rgba(139,92,255,.2);border-radius:10px;cursor:pointer;transition:all var(--tr);margin-top:16px;font-size:.8125rem;color:var(--secondary);font-weight:600}
.bonus-trigger:hover,.bonus-trigger:focus-visible{background:rgba(139,92,255,.15);border-color:rgba(139,92,255,.4);outline:2px solid var(--secondary);outline-offset:2px}
.bonus-trigger .icon{font-size:1.25rem;animation:pulse-glow 2s ease-in-out infinite}
.bonus-content{display:none;margin-top:12px;padding:16px;background:rgba(139,92,255,.06);border:1px solid rgba(139,92,255,.15);border-radius:10px;font-size:.875rem;color:var(--text);line-height:1.6}
.bonus-content.open{display:block}
.bonus-trigger{width:100%;font-family:inherit;text-align:left}
.bonus-xp-note{margin:-4px 0 8px!important;padding:10px 12px;border-radius:8px;background:rgba(255,184,77,.07);border:1px solid rgba(255,184,77,.18);color:var(--warning)!important;font-size:.8125rem!important}
.bonus-xp-note.complete{background:rgba(66,211,146,.08);border-color:rgba(66,211,146,.25);color:var(--success)!important}
@keyframes pulse-glow{0%,100%{opacity:1}50%{opacity:.5}}

/* Demo lesson hero and relativity simulation */
.demo-hero{position:relative;margin:4px 0 22px;border-radius:14px;overflow:hidden;border:1px solid rgba(108,246,255,.2);background:#080d1b;box-shadow:0 18px 45px rgba(0,0,0,.28)}
.demo-hero img{display:block;width:100%;height:auto;aspect-ratio:2/1;object-fit:cover}
.demo-hero-glow{position:absolute;inset:auto 12% -35% 12%;height:50%;background:radial-gradient(ellipse,rgba(79,140,255,.32),transparent 70%);pointer-events:none}
.relativity-sim{position:relative;background:linear-gradient(180deg,#080d1b,#0d1529);border-radius:14px;overflow:hidden;margin:16px 0;border:1px solid rgba(108,246,255,.2);box-shadow:inset 0 1px 0 rgba(255,255,255,.03),0 14px 32px rgba(0,0,0,.18)}
.rel-legend{display:flex;flex-wrap:wrap;gap:8px 16px;padding:11px 14px;background:rgba(21,28,51,.78);border-bottom:1px solid rgba(108,246,255,.1);font-size:.6875rem;color:var(--text-muted)}
.rel-legend span{display:inline-flex;align-items:center;gap:6px}
.rel-dot{width:8px;height:8px;border-radius:50%;box-shadow:0 0 8px currentColor}
.rel-dot-flash{color:#FFB84D;background:#FFB84D}.rel-dot-platform{color:#A855F7;background:#A855F7}.rel-dot-train{color:#42D392;background:#42D392}
.rel-status{min-height:42px;padding:10px 16px;font-size:.75rem;color:var(--accent);text-align:center;background:rgba(21,28,51,.72);border-top:1px solid rgba(108,246,255,.1);line-height:1.45}
.rel-controls{display:grid;grid-template-columns:1fr auto;gap:8px;margin:12px 0}
.rel-controls .btn{padding:10px 14px;border:1px solid rgba(108,246,255,.25);background:rgba(79,140,255,.07);color:var(--accent)}
.rel-controls .btn:hover,.rel-controls .btn:focus-visible{border-color:var(--accent);outline:2px solid var(--accent);outline-offset:2px}

/* Reward screen */
.reward-screen{text-align:center}
.reward-screen .xp-big{font-size:3rem;font-weight:700;color:var(--accent);margin:24px 0 8px;display:flex;align-items:center;justify-content:center;gap:8px}
.reward-screen .xp-big .xp-icon{height:48px;width:48px;flex-shrink:0;object-fit:contain}
.reward-screen .xp-label{font-size:1rem;color:var(--text-muted);margin-bottom:32px}
.star-row{display:flex;justify-content:center;gap:12px;margin-bottom:24px}
.star{font-size:2rem;opacity:.2;transition:all .4s ease}
.star.earned{opacity:1;transform:scale(1.2)}

/* Perfect reward */
.reward-perfect{position:relative}
.reward-perfect .star-row .star{color:#FFD700;text-shadow:0 0 16px rgba(255,215,0,.6),0 0 40px rgba(255,215,0,.3);animation:star-glow 2s ease-in-out infinite alternate}
.reward-perfect .star-row .star:nth-child(2){animation-delay:.3s}
.reward-perfect .star-row .star:nth-child(3){animation-delay:.6s}
@keyframes star-glow{0%{transform:scale(1.2);filter:brightness(1)}100%{transform:scale(1.35);filter:brightness(1.3)}}
.star-sparkle{position:absolute;width:4px;height:4px;background:#FFD700;border-radius:50%;opacity:0;top:50%;left:50%;animation:sparkle-burst 1.2s ease-out var(--delay,.0s) forwards}
@keyframes sparkle-burst{0%{opacity:1;transform:translate(0,0) scale(1)}50%{opacity:.7}100%{opacity:0;transform:translate(var(--tx,30px),var(--ty,-20px)) scale(0)}}

/* Retry hint */
.retry-hint{text-align:center;margin:0 0 20px;padding:16px 20px;background:rgba(245,158,11,.06);border:1px solid rgba(245,158,11,.15);border-radius:10px}
.retry-hint-text{font-size:.9rem;font-weight:600;color:#F59E0B;margin-bottom:4px}
.retry-hint-sub{font-size:.75rem;color:var(--text-muted);margin-bottom:12px}
.retry-hint-btn{font-size:.8125rem;padding:8px 20px;border:1px solid rgba(245,158,11,.3);color:#F59E0B;border-radius:8px;text-decoration:none;display:inline-flex;align-items:center;gap:6px;transition:all .2s}
.retry-hint-btn:hover{background:rgba(245,158,11,.1);border-color:#F59E0B;color:#F59E0B}
@media(prefers-reduced-motion:reduce){.reward-perfect .star-row .star{animation:none;transform:scale(1.2)}.star-sparkle{animation:none;display:none}}

/* Animations */
@keyframes shake{0%,100%{transform:translateX(0)}20%,60%{transform:translateX(-6px)}40%,80%{transform:translateX(6px)}}
.shake{animation:shake .4s ease}

/* Simulations */
.sim-box{margin:20px 0;padding:16px;background:var(--bg-card);border-radius:8px;border:1px solid var(--border)}
.sim-canvas{display:block;margin:0 auto;width:100%;max-width:300px;background:#1a2f4a;border-radius:6px}
.sim-controls{margin-top:16px;display:flex;flex-direction:column;gap:12px}
.sim-row{display:flex;align-items:center;gap:12px}
.sim-row label{flex:0 0 auto;white-space:nowrap;font-size:.875rem}
.sim-row input[type=range]{flex:1;min-width:0}
.sim-row .sim-formula{flex:0 0 auto;font-size:.85rem;color:var(--text-muted);white-space:nowrap}
.sim-reset{width:100%;margin-top:4px}

/* AI Teacher */
.ai-teacher-btn{position:absolute;top:12px;right:12px;width:40px;height:40px;border-radius:50%;border:none;background:transparent;cursor:pointer;display:flex;align-items:center;justify-content:center;transition:all var(--tr);z-index:5;padding:0;animation:ai-glow 3s ease-in-out infinite}
.ai-teacher-btn img{width:100%;height:100%;object-fit:contain;border-radius:50%}
.ai-teacher-btn:hover{transform:scale(1.15);filter:brightness(1.3)}
.ai-teacher-btn:active{transform:scale(0.95)}
@keyframes ai-glow{0%,100%{filter:brightness(1);box-shadow:0 0 8px rgba(108,246,255,.15)}50%{filter:brightness(1.2);box-shadow:0 0 20px rgba(108,246,255,.4),0 0 40px rgba(139,92,255,.2)}}

/* AI Question */
.ai-question-btn{position:absolute;top:16px;right:56px;width:28px;height:28px;border-radius:50%;border:none;background:transparent;cursor:pointer;display:flex;align-items:center;justify-content:center;z-index:5;padding:0;transition:all var(--tr)}
.ai-question-btn::before{content:'?';background:linear-gradient(135deg,var(--primary),var(--accent),var(--secondary),var(--primary));background-size:300% 300%;-webkit-background-clip:text;-webkit-text-fill-color:transparent;background-clip:text;animation:question-gradient 4s ease infinite;font-size:1.5625rem;font-weight:800;line-height:1}
.ai-question-btn:hover{transform:scale(1.2);filter:drop-shadow(0 0 6px rgba(108,246,255,.4))}
.ai-question-btn:active{transform:scale(0.9)}

/* Tooltips */
.has-tooltip::after{content:attr(data-tooltip);position:absolute;top:calc(100% + 6px);right:0;background:rgba(21,28,51,.95);color:#E2E8F0;font-size:.75rem;font-weight:500;padding:5px 10px;border-radius:6px;white-space:nowrap;pointer-events:none;opacity:0;transform:translateY(-4px);transition:opacity .2s ease,transform .2s ease;border:1px solid rgba(79,140,255,.15);z-index:6}
.has-tooltip:hover::after{opacity:1;transform:translateY(0)}
@keyframes question-gradient{0%{background-position:0% 50%}50%{background-position:100% 50%}100%{background-position:0% 50%}}

/* AI Teacher Modal */
.ai-teacher-modal{display:none;position:fixed;top:0;left:0;right:0;bottom:0;z-index:1000}
.ai-teacher-modal.active{display:flex}
.ai-teacher-modal-backdrop{position:absolute;top:0;left:0;right:0;bottom:0;background:rgba(0,0,0,.6);backdrop-filter:blur(4px)}
.ai-teacher-modal-container{position:relative;width:90%;max-width:500px;background:var(--bg-card);border:1px solid var(--border);border-radius:var(--radius-lg);box-shadow:0 20px 60px rgba(0,0,0,.3);display:flex;flex-direction:column;max-height:90vh;overflow:hidden;margin:auto}
.ai-teacher-modal-header{display:flex;align-items:center;justify-content:space-between;padding:20px 24px;border-bottom:1px solid var(--border)}
.ai-teacher-modal-header h2{font-size:1.25rem;font-weight:700;color:var(--text-heading);margin:0;display:flex;align-items:center;gap:10px}
.ai-teacher-modal-header h2 img{width:28px;height:28px;object-fit:contain;border-radius:50%}
.ai-teacher-close{width:32px;height:32px;border:none;background:none;color:var(--text-muted);cursor:pointer;font-size:1.5rem;display:flex;align-items:center;justify-content:center;transition:all var(--tr)}
.ai-teacher-close:hover{color:var(--text);transform:scale(1.2)}
.ai-teacher-modal-content{flex:1;overflow-y:auto;padding:24px;font-size:.9375rem;line-height:1.7;color:var(--text)}
.ai-teacher-spinner{width:40px;height:40px;border:3px solid rgba(79,140,255,.2);border-top-color:var(--primary);border-radius:50%;animation:spin 1s linear infinite;margin:0 auto}
.ai-teacher-spinner.hidden{display:none}
@keyframes spin{to{transform:rotate(360deg)}}
.ai-teacher-text{color:var(--text);line-height:1.8}
.ai-teacher-text p{margin-bottom:12px}
.ai-teacher-text p:last-child{margin-bottom:0}
.ai-error{background:rgba(255,94,122,.08);border:1px solid rgba(255,94,122,.25);border-radius:8px;padding:12px 16px;color:var(--danger);font-size:.875rem}
.ai-teacher-modal-actions{display:flex;gap:12px;justify-content:center;padding:16px 24px;border-top:1px solid var(--border);background:var(--bg-card)}
.ai-teacher-modal-actions button{background:var(--primary);color:#fff;padding:10px 24px;border:none;border-radius:8px;font-size:.875rem;font-weight:600;cursor:pointer;transition:all var(--tr);font-family:inherit;line-height:1.4}
.ai-teacher-modal-actions button:hover{background:#6BA0FF;box-shadow:0 0 16px rgba(79,140,255,.3)}
.ai-teacher-modal-actions button.ai-teacher-btn-secondary{background:transparent;color:var(--primary);border:1px solid rgba(79,140,255,.3)}
.support-buttons{display:flex;gap:12px;margin-top:8px}
.btn-support{flex:1;display:inline-flex;align-items:center;justify-content:center;gap:10px;padding:12px 20px;border-radius:12px;font-size:.9rem;font-weight:700;letter-spacing:.04em;text-transform:uppercase;text-decoration:none;transition:all 200ms ease;border:none}
.btn-support svg{width:24px;height:24px;flex-shrink:0}
.btn-patreon{background:linear-gradient(135deg,#3D1F6E 0%,#5C2D91 50%,#7B3FA0 100%);color:#fff}
.btn-patreon:hover{box-shadow:0 4px 24px rgba(92,45,145,.45);filter:brightness(1.1)}
.btn-boosty{background:linear-gradient(135deg,#E8600A 0%,#F47B20 50%,#F89838 100%);color:#fff}
.btn-boosty:hover{box-shadow:0 4px 24px rgba(244,123,32,.45);filter:brightness(1.1)}
.ai-teacher-modal-actions button.ai-teacher-btn-secondary:hover{background:rgba(79,140,255,.15);border-color:var(--primary)}

/* KaTeX */
.katex{color:var(--accent)}
.math-display{text-align:center;margin:16px 0;overflow-x:auto;overflow-y:hidden;-webkit-overflow-scrolling:touch}
.math-display .katex-display{margin:0}
.math-inline .katex{font-size:1em}
.katex-display{overflow-x:auto;overflow-y:hidden;padding:4px 0;-webkit-overflow-scrolling:touch}

/* Responsive */
@media(max-width:600px){
    .card-area{padding:20px 16px}
    .card{padding:32px 20px}
}
@media(max-width:480px){
    .top-bar{gap:8px;padding:10px 12px}
    .exit-btn,.back-btn{width:28px;height:28px;min-width:28px}
    .progress-track{height:5px}
    .xp-badge{font-size:.6875rem;gap:3px}
    .xp-icon{height:2em}
    .card-area{padding:16px 12px}
    .card{padding:24px 16px;position:relative}
    .card h2{font-size:1.125rem}
    .card p{font-size:.875rem}
    .card-actions{flex-wrap:wrap}
    .btn{padding:10px 20px;font-size:.875rem}
    .option{padding:12px 14px;font-size:.875rem}
    .match-grid{grid-template-columns:1fr}
    .sim-row{flex-wrap:wrap}
    .sim-row label{flex:1 0 100%;margin-bottom:2px}
    .sim-row input[type=range]{flex:1 1 100%}
    .sim-row .sim-formula{flex:1 0 100%;text-align:center;margin-top:4px}
    .ai-teacher-btn{width:34px;height:34px;top:10px;right:10px}
    .ai-question-btn{width:32px;height:32px;top:12px;right:48px}
    .ai-teacher-modal-container{width:95%;max-height:85vh}
    .ai-teacher-modal-actions{flex-wrap:wrap}
    .ai-teacher-modal-actions button{flex:1;min-width:0}
    .reward-screen .xp-big{font-size:2rem;gap:6px}
    .reward-screen .xp-big .xp-icon{height:36px;width:36px}
    .star{font-size:1.5rem}
}

#path-canvas:focus-visible{outline:3px solid var(--accent);outline-offset:3px}

/* Native modal keeps keyboard focus inside the exit choices. */
#lesson-exit-dialog { color: var(--text); background: var(--bg-card); border: 1px solid var(--accent); border-radius: 20px; padding: 24px; width: min(480px, calc(100vw - 32px)); max-height: calc(100dvh - 32px); overflow: auto; margin: auto; }
#lesson-exit-dialog::backdrop { background: rgb(0 0 0 / 70%); }
#lesson-exit-body { margin: 16px 0; line-height: 1.6; }
#lesson-exit-error, #lesson-exit-save-error { color: #ff8080; margin-bottom: 16px; }
.exit-actions { display: flex; flex-direction: column; gap: 12px; }
.exit-actions button:focus-visible { outline: 3px solid var(--accent); outline-offset: 3px; }